Applicants claim priority under 35 U.S.C. xc2xa7119 of Russian Application No. 99122270, filed Oct. 27, 1999. Applicants also claim priority under 35 U.S.C. xc2xa7365 of PCT/RU00/00419 filed Oct. 24, 2000. The international application under PCT article 21 (2) was not published in English.
The invention relates to drying equipment and can be used in timber industry, woodworking and other branches of industry, whenever parameters and procedures necessary to dry materials as wood are used.
Drying plants are known from prior art that include a batch-operating drying chamber and a furnace located near it, in which woodworking waste products may be and are primarily used as fuel to generate heat necessary for drying. Usually, the furnace gases or a mixture of furnace gases with air are used in such systems (e.g., see, Spravochnik po sushke drevesiny (Wood-drying reference book) edited by E. S. Bogdanov, Moscow, Lesnaya promyshlennost, 1990, pp. 38-63, patent RU 2105941, and the following inventor""s certificates: SU:380454, JP09223628, JP11094460, JP11201639, JP11241883). While using those systems, accompanying problems inevitably appear due to the following facts. Gaseous combustion products of high-temperature wood burning consist largely of CO2, H2O and nitrogen oxides NOx. The situation becomes much more complicated when an incomplete fuel combustion takes place, because in this case the combustion products are fouled not only with soot (i.e., unburned carbon particles), but also with dry distillation products as well, consisting of CO and a number of hydrocarbons, which are usually chemically active, smell specifically, have relatively low temperatures of boiling, etc. Furthermore, there is a risk of environmental pollution due to a possible formation of dioxins and furans as a result of condensation reactions, when gaseous products of wood burning are cooled with the presence of even minimal amounts of chlorine (although furnace ashes do not contain these products).
As a result, to ensure ecological safety of the drying plants and to produce high-quality dry wood materials, considerable expenses are required to purify combustion products and drying agents. Besides, special devices are required to provide necessary drying conditions (e.g., different humidifiers or steam generators are used to maintain the necessary level of humidity), resulting in a sophisticated design, higher prices and complicated maintenance. Nevertheless, neither the measures taken nor considerable expenses can guarantee either necessary ecological safety or high quality of dried materials.
The subject of the present invention is to ensure higher ecological safety and provide a highly productive, power-saving drying process, allowing to produce high quality dried materials. The proposed drying plant is not expensive, simple in maintenance and does not require highly qualified personnel. The drying plant can be installed either in existing premises or in the form of a separate premise, e.g. at lumbering sites.
The proposed drying method is as follows: stack the wood into the free internal space of the drying chamber, close the chamber, and supply a hot drying agent (the air heated in the pipes located in the furnace flue) into the chamber. The woodworking waste products are the primary fuel used in the furnace. The air is forcedly circulated from pipes located in the furnace flue to the lower part of the free internal space of the drying chamber, and from the upper part of the free internal space of the drying chamber into the pipes of the furnace flue, and backwards. During drying, a portion of cooled and humidified air from the upper part of the free internal space of the drying chamber is forcedly supplied into the condensate cleaning unit, where it is mixed with the furnace gases, which are also forcedly supplied into the unit for purification; on their way to the cleaning unit, the furnace gases pass through a cavity located in the bottom of the drying chamber providing additional heating of the chamber. Air circulation from the pipes of the furnace flue to the lower part of the free internal space of the drying chamber and from its upper part into the pipes located in the furnace flue, and forced supply of furnace gases through an exhaust pipe into the cavity in the bottom of the drying chamber and then into the condensate cleaning unit, as well as forced supply of a portion of cooled and humidified air from the upper part of the free internal space of the drying chamber into the condensate cleaning unit, is realized with the aid of three appropriate exhaust ventilators. The pressure in the free internal space of the drying chamber falls slightly during drying. Humidity conditions can be adjusted by releasing vapor from the upper part of the free internal space of the drying chamber into atmosphere.
Temperature conditions can be regulated by adjusting air circulation intensity from the pipes of the furnace flue to the lower part of the free internal space of the drying chamber and from the upper part of the free internal space of the drying chamber into the pipes; temperature conditions can also be regulated by adjusting the temperature of the drying agent (air), which depends on burning intensity and the amount of fuel in the furnace.
The proposed method for drying wood may be realized as a drying plant consisting of a heat-insulated drying chamber with a free internal space, a furnace located close to the drying chamber, and facilities for supplying drying agent from the furnace into the drying chamber. The bottom of drying chamber is designed with two cavities horizontally arranged and hermetically separated from each other. The partition between these cavities is made of diathermic material. The lower cavity in the bottom of the drying chamber is designed in such a way as to provide forced feeding of furnace gases into the cavity from the exhaust pipe of the furnace flue. The upper cavity located in the bottom of the drying chamber is designed in such a way as to provide supply of the air heated in the furnace flue into the cavity; in the upper cavity, the heated air is distributed among air distribution channels to interact with the material to be dried located in the free internal space of the drying chamber at specially arranged places. There is a possibility to provide forced feeding of a portion of the air cooled and humidified during drying from the upper part of the free internal space of the drying chamber into the furnace flue. Besides, the drying plant is equipped with a condensate cleaning unit located outside the drying chamber; the furnace gases are forcedly fed into the unit after they pass through the lower cavity in the bottom of the drying chamber; also, a portion of cooled and humidified air is forcedly fed into the unit from the upper part of the free internal space of the drying chamber for mixing up with the furnace gases to form a condensate; after that, the purified air is exhausted into atmosphere.
The facilities that forcedly supply furnace gases from the exhaust pipe of the furnace flue to the lower cavity in the bottom of the drying chamber and into the condensate cleaning unit after they pass through the lower cavity, are designed in the form of the first exhaust ventilator (smoke exhauster) located outside the drying chamber and condensate cleaning unit and connected to the outlet of the lower cavity in the bottom of the drying chamber and to the inlet of the condensate cleaning unit.
The facilities that supply a portion of cooled and humidified air from the upper part of the free internal space of the drying chamber into the condensate cleaning unit are designed in the form of the second exhaust ventilator located outside the drying chamber and the condensate cleaning unit and connected to both of them.
The facilities that bleed a portion of cooled and humidified air from the upper part of the free internal space of the drying chamber and supply it into the furnace flue are designed in the form of the third exhaust ventilator connected both to the drying chamber and the furnace flue so as to provide the closed air circulation from the upper part of the free internal space of the drying chamber into the furnace flue and from the furnace flue into the upper cavity in the bottom of the drying chamber and further into the free internal space of the drying chamber.
A casing of the third exhaust ventilator is connected to an outgoing pipe intended to discharge into atmosphere moisture which is accumulated on the internal surface of the casing as a result of condensation of cooled and humidified air bled by the third exhaust ventilator from the upper part of the free internal space of the drying chamber. The outgoing pipe is equipped with a shutter to adjust humidity conditions of the drying process. The furnace flue contains a pipe where the air is heated by the furnace gases and then fed into the drying chamber and backwards, thus supporting the process of drying. The pipe is curved many times to increase the way and time for the air to go through the furnace flue, enabling maximum heat transfer from the furnace gases to the air in the pipe.
A shutter for adjusting temperature conditions of the drying process is installed in the channel, designed for forced air supplying from the upper free space of the drying chamber into the furnace flue.
The lower cavity in the bottom of the drying chamber is equipped with at least two partitions to provide labyrinth passing of furnace gases. It increases heat emission from the furnace gases to the walls of the lower cavity, and therefore, provides additional heating of the drying chamber.
The air distribution channels are perpendicular to the direction of the heated airflow fed into the upper cavity in the bottom of the drying chamber. These channels are located between and along the areas for placing the material to be dried; each air distribution channel is separated with a vertical partition from an adjacent area for placing the material to be dried.
The areas for placing the material to be dried are located on/above the upper surface of the diathermic partition between the upper and lower cavities in the bottom of the drying chamber so as to allow heated air to pass through the material to be dried while moving up to the upper part of the free internal space of the drying chamber. The areas for placing the material to be dried are equipped with the vertical partitions to direct and distribute the heated air. First, the heated air passes the free space of the upper cavity in the bottom of the drying chamber through the air distribution channels, and then it is supplied to the material being dried.
There is an additional possibility to supply heated air to the material being dried via the through holes in the vertical partitions that separate the areas for placing the material to be dried from the air distribution channels. These holes have different diameters that increase along the way of heated air passage via the air distribution channels. These holes are equipped with shutters.
In the upper surface of the upper cavity in the bottom of the drying chamber, close to one of its lateral walls, there are the through holes, which provide additional hot air supply from the upper cavity in the bottom of the drying chamber into the free internal space of the drying chamber. In case the drying chamber is used for drying saw-timber piles, which is located along the air distribution channels, the through holes are made near the ends of the piles.
When the drying chamber is not completely loaded, it is possible to close the air distribution channel adjacent to the area for placing the material to be dried, which contains no material.
The condensate cleaning unit is designed in the form of a hollow reservoir to ensure condensation on its internal walls, when cooled and humidified air fed from the upper part of the free internal space of the drying chamber gets mixed up with the furnace gases from the lower cavity in the bottom of the drying chamber.
The power capacity of the third exhaust ventilator is higher than the power capacity of the second exhaust ventilator. The volume of the free internal space of the drying chamber determines the values and ratios of the power capacities of the second and third ventilators.